This invention relates to the examination of articles for defects, and more specifically to a method of conducting an eddy current surface examination of a metal component that is coated or covered with a nonmetallic material for purposes of detecting therein, without the necessity of removing the coating or covering from the component, cracks that are of at least a preestablished minimal dimension.
There are known to exist many instances wherein it is desirable and/or necessary to effect a surface examination of an operating component. Notwithstanding the number of such instances and the differences that exist therebetween, in general one finds that the reason for conducting such a surface examination is associated in some manner with the need to determine the relative operating condition of the component in question. That is, commonly there exists a need to ensure the operability of the component preparatory to its being placed in service and/or the need periodically to verify that the component is still in good working order. To this end, it is not uncommon to find that standards have been promulgated in this regard for various kinds of operating components. Namely, these standards which have been promulgated serve to establish the nature and/or extent of the surface defects which will be deemed to render a particular type of operating component unserviceable.
By way of exemplification and not limitation, reference is had here to rotary members, as being representative, generally, of one such form of component. Further, one specific type of rotary member to which reference may be made in this connection is that of fly-wheels, and in particular flywheels of the sort, which often are found cooperatively associated with the coolant circulation pump motors that are employed in nuclear steam supply systems. The function which flywheels perform in this type of a nuclear-related application is that of assisting in the accomplishment of coastdown of the coolant circulation pump motors. As such, it is, therefore, important that when the flywheels are needed that they be capable of functioning in their intended manner. To this end, obviously one way of ensuring that the flywheels are in good working order is to periodically conduct an examination of the flywheels for defects. Moreover, rather than depending on compliance with some voluntary schedule of examination of such components, it is known that in a number of instances governmental authorities have promulgated regulations that mandate the performance of such periodic examination with regard to particular components for purposes of effecting a detection of defects therein that could impair the operativeness of the component. This is prticularly true in the case of many of the operating components of a nuclear steam supply system.
With specific regard to flywheels of the sort referred to above, i.e., the large flywheels needed for coastdown in nuclear reactor coolant circulation pump motors, existing governmental regulations require that they undergo surface examination during preservice and at ten year intervals during the life of the nuclear plant in which they are installed. The performance of such a surface examination on such flywheels is rendered more difficult by virtue of the fact that these flywheels are normally painted to provide them with corrosion protection against the high humidity environment to which they are subjected. Thus, for purposes of accomplishing such surface examinations there has existed a need in the past for removing the flywheels from the motors followed by the sand blasting thereof down to the base metal surface to remove the paint therefrom.
Note should be taken here of the fact that in requiring that surface examinations be performed on such flywheels, governmental regulations have not only specified the frequency of such examinations and the nature of the defects which the surface examination was intended to detect, but have also dictated the manner in which the examination is to be performed. Namely, such governmental regulations have heretofore required that the surface examination be conducted in accordance with the procedures that are found set forth in the applicable industrial codes, which have been promulgated governing the performance of surface examination on metal components.
In this regard, until now in order to comply with governmental regulations the surface examination of flywheels of the type being discussed herein has had to be performed by either of two techniques. That is, the only techniques acceptable for use for this purpose have been those of dye penetrant and magnetic particle. Both of these, however, require that the examination be conducted on a clean base metal surface. Accordingly, when the component that is to be examined, as in the case of the subject flywheels, has had a coating or a covering applied thereto, the removal of the latter must first be effected before the dye penetrant or magnetic particle inspection thereof can be had. In the case of flywheels associated with reactor coolant circulation pump motors this has meant that during a refueling or maintenance outage significant time and manpower has had heretofore to be expended in the disassembly of the motors, flywheel removal and subsequent surface preparation for the examination, not to mention the necessity of constructing special facilities for the sand blasting. Presently, this cycle of motor disassembly, flywheel cleaning, examination and reassembly requires about seven days to complete per flywheel exclusive of the time required for evaluation of the examination results. This seven days in turn represents motor downtime as well as radiation exposure time for the workers involved in performing these tasks. As regards motor downtime, recognition must be had of the fact that in order to accomplish the removal of the flywheel, etc., the motor must be sufficiently disassembled such that it cannot readily be placed back in service should a need therefor arise.
In addition to the disadvantages enumerated above that are associated with the use of the techniques of dye penetrant and magnetic particle for purposes of performing surface examinations of metal components, there are also other disadvantages associated with the usage thereof. For example, in the case of the subject flywheel, a surface examination is commonly made at the time of the completion of the manufacture thereof. Thereafter, when the flywheel reaches the site whereat it is to be employed, the flywheel normally would undergo yet another surface examination, i.e., a preservice surface examination. Finally, surface examinations will be conducted periodically on the flywheel after it has been placed in service. To the extent the flywheel for purposes of each of these surface examinations must be disassembled from the motor, and must have removed therefrom the corrosion protective coating that has been applied thereto, the possibility arises that inconsistencies can develop in the results obtained from the surface examination that are occasioned by the treatment to which the flywheel is subject in preparation for the surface examination, rather than being representative of the condition of the flywheel at the time just prior to the commencement of the preparation of the flywheel for examination. Further, such inconsistencies can obviously lead one to arrive at misleading conclusions concerning the operative state of the flywheel. Secondly, in the course of effecting the removal of the corrosion protective coating from the flywheel there is commonly a need to make use of solvents, etc. In addition, paint chips are commonly produced. Such solvents and/or paint chips, etc. can detrimentally affect the performance and/or operation of the motor should they become captured therewithin, particularly in view of the relatively high precision nature of such equipment. A need has thus been shown to exist in the prior art for the development of a new and improved technique that would be operative for purposes of conducting surface examinations on coated metal components, and which would not necessitate for its use the removal of the coating from the metal component. Secondly, such a new and improved technique should be capable of use for purposes of effecting a detection from such surface examination of defects in accordance with the requirements established for such detection by existing governmental regulations. Thirdly, such a new and improved technique must be capable of being accepted under the applicable industrial codes as a technique that is recognized for use for the performance of surface examinations on metal components.
It is, therefore, an object of the present invention to provide a new and improved method for effecting a surface examination of a component.
It is another object of the present invention to provide such a method which is particularly applicable for use for purposes of effecting surface examinations of coated metal components.
It is still another object of the present invention to provide such a method for effecting a surface examination of a coated metal component which does not necessitate the removal of the coating from the component for purposes of effecting the surface examination thereof.
A further object of the present invention is to provide such a method which makes use of eddy current means for purposes of effecting a surface examination of a coated metal component.
A still further object of the present invention is to provide such a method which is capable of being used to effect from a surface examination of a coated metal component the detection of defects in accordance with the requirements established for such detection by existing governmental regulations.
Yet another object of the present invention is to provide such a method for effecting a surface examination of a coated metal component which has achieved acceptance under the applicable industrial codes as a technique that is recognized for use for the performance of such surface examinations.
Yet still another object of the present invention is to provide such a method for effecting a surface examination of a coated metal component which is relatively easy to employ and which enables significant economies of time and manpower to be realized through the use thereof as compared to that required when utilizing prior art techniques.